Volume control



Patented Oct. 28, 1930 PATE Nr OFFICE JOHN M. MILLER, F PHILADELPHIA, PENNSYLVANIA, ASSIGNOR TO ATWATER KENT MANUFACTURING COMPANY, 0F PHILADELPHIA,

OF PENNSYLVANIA.

Application led June 28,

invention relates to the control of volume or magnitude of amplification in radio Vreceiving systems, and more particularly l prised of coil layers or windings of bare resistance conductor disposed with the turns of one contacting, overlying and crossing or intersecting those of another; preferably the layers or coils are reversely wound, in the sense that the conductor helices progress axially in opposite directions; and, preferably, the pitch, or spacing between turns, is different in or for the different layers or coils. More specifically, an end of resistance wire is secured to a suitable form, as a thin strip of flexible insulating material, as intermediate its ends, and after the wire is wound thereon with a variable or fixed pitch or spacing towards one end Vof the form, the direction of winding is changed and the wire with same or different and preferably lesser pitch or spacing is wound back-over and upon the first winding or layer.

Further in accordance with my invention, the resistance described is one of several components of a resistance unit and is that section corresponding to and producing control in the low volume region ;more specifically, the unit comprises at least two other sections andthe spacing of turns is the greater in that' of the two sections nearest to the low volume section; preferably the lengths or resistances of the sections with respect to each other and to the total resistance are such that the percent change in resistance, as a co-operating control contact moves from one section to another, is suitably small to avoid clicks or like noises in the loud speaker.

My invention resides in the method and apparatus hereinafter described and claimed.

For an understanding of some of the various forms my invention may take, reference is to be had to the accompanying drawings in which: y

PENNSYLVANIA, A CORPORATION VOLUME coN'rRoL 192s. serial No. 289,012.

Fig. 1 is a diagrammatic view of a receiv ing system embodying my invention.

Fig. 2 is a side elevational view of a resistance unit.

Fig. 3 is a diagrammatic view of mechaJ nism for winding the resistance unit of Fig. 2.

Figs. 4 and'eta are side elevational views of a modified form of resistance unit in different steps of its manufacture.

Fig. 5 is an elevational view, partly in section, illustrative of the mounting of the resistance unit and its co-acting control contact.

Fig. 6 is an end elevational view of the structure shown in Fig. 5.

Fig. '7 modified form.

Referring to Fig. l, the received electroradiant energy is absorbed by the antenna A or other equivalent absorption structu-re. In the example illustrated V is a thermionic radio frequency amplifier tube utilized as'a coupling tube in the first stage of a cascade of radio frequency amplifying, detecting and audio frequency amplifying tubes. Its grid g is connected to a terminal of coupling eleis a fragmentary View of a further ment or transformer 'I while its cathode or l filament 7 is connected to earth or'counter capacity E through the condensers 7c which exhibit low reactance at the radio frequencies involved. The transformer 'I maybe an auto-transformer having a step-up ratio substantially as described and ,claimed in` co-pending Miller application Serial N o. 263,272, inea March 21,1928.

In the circuit of the anode or plate a of the l tube V is the primary P of a radio frequency transformer T1, preferably having high stepup ratio and whose secondary S is shunted by the variable tuning condenser C.- The second! 4cycle alternating current, connected tothe rimary of the transformer T2.` A secon ary winding of the transformer supplies so-called raw alternating current to the filament or heating element fof the tube V, and of other tubes notvshown. B represents a sourceof anode circuit current, which too may be derived from source G through a rectilier- `lilter system. The resistance R1, which is common to the input and output Circuits of the tube V, and is traversed by the direct current' flowing intol the anode circuit, serves to bias the grid g to a suitable negative potential.

The volume control resistance R2 i's preferably connected, as shown, with one terminal connected byA conductor 26 to winding T at the antenna connection thereto, and with its other terminal connected through conductor 26a `to thatterminal of winding T remotev from gridl g.

Movable along theresistance is the control Contact K connected by conductor 32 to earth E. By moving the 'contact K-along the resistance R2 there is produced a variable effect upon the input system of the tube V, which.

decreases the signal potential impressed upon grid g as the contact K is moved toward the antenna connection to the transformer T, as viewed in Fig. l, and vice versa. Accordingly the signal energy impressed upon the tube V is varied, with resultant control of the amplitude of signal energy in the output circuit thereof and ultimately in the volume of sound emitted by the loud speaker.

- contact with each other.

This type of lcontrol of volume is particularly adapted for use in radio receivlng -sets utilizing thermionic` tubes one or more of whose electrode circuits are energized. froma source of alternating current; in such receiving sets, to avoid hum, it is desirable toprocure volume'control without recourse to control of filament or heater current, and without recourse to control of anode current.

The conductorof the resistance R2 is preferably of high specific resistance, such as Advance wire, or the like. The spacing of the.

vin contact with each other. The turns c and d are not parallel, but intersect or cross each other, and where they cross they electrically The eectof moving the contact K along the edge of section r3,

is substantially similar to. that of moving the contact continuously along the coarsely spaced turns' c with gradual and smooth change of resistance. It is impractical or undesirable because of considerations of space and structure to maintain engagement of contact K with and along the wire c. With the turns of the conductor d, spaced considerably closer than and overlying and crossing the 'turns of c, engagement of the contact K with the successive turns of d amounts to successive connections between the contact K and numerous points along the conductor c through numerous successive lresistance conductors, each a part of the conductor d and extending from the edge of the unit to the point of intersection Aand contactwith conductor 0. A

As indicated in Fig. 2, the conductor of the resistance R2 is wound in the form of a helix upon the thin or fiat strip, plate or form 3 of insulating material. As indicated the sections r1 and r2 have their turn differently spaced,-and r3 comprises wire c having in effect a large number of taps d therefrom, with theresult that per unit length along the edge of unit R2 theresistance change is greatest in section r1, less in section r2, and still less in section r3. For example, the section 1'1 may be 41A inches long, 120 turns per inch; the sec- 'tion r2 may be of an inch long, 60 turns per inch, and section r3 one inch long, layer c 71/2 turns per inch, underlying and contacting at intervals with coil d 60 turns per inch. The

spacing of the turns of a -section need not be uniform throughout but may, for example, increase as `section r3 is approached, as in copending application Serial No. 249,785, filed January 27, 1928. The conductor throughout the several sections may be Advance o'r other suitable Wire, about No. 34 B and S gauge. When the strip 3 is 1/ inch Wide and about of an inch thick, the entire resistance of the three sections is about 530 ohms.

'The resistance R2 of Fig. 2 is wound by looping one end of resistance wire through a hole 4 spaced a suitable distance from the end 1 of the strip 3, anda suitable number of widely spaced turns c are Wound on the form towards the end l, whereupon the direction of winding is reversed toward end 2 and the turns d are more closely spaced during Winding over the underlying conductor layer c, to complete section'ra; and winding l is Acontinued to form the section r2; thereafter the pitch is further decreased, to produce greater resistance change per unit of movement of contact K, and the winding is continued towards the end 2 of the strip where the end of the resistance wire is looped through a hole '5 or otherwise suitably anchored, so completing section 1'1. The end clips 6, 6 of thin conducting material and having bent overears 6a, .62, are then clipped over the respective ends of the form, the holes 7 7 thereof in re 'ster with the holes 8, 8 of the strip 3 an with the inner edgeof the right hand clip 6 preferably in contact with the last turn of coil fof resistance sec- 4.tion r3, substantially at the point at which l it passes over that edge of the resistance unit with which contact K is in engagement.

j The resistance R2 is conveniently Woundby holding and rotating the form 3 between and by two rotatable spindles 9 and 10, Fig.l 3,

and at least 'one of which is driven, as by a motor M, through gears 11, 12, 13 and 14. On the shaft of gear 12 may be mounted a leadA or master screw N having two connected threads, D, for section "r, E of diiferent sistancev Wire from the spool e through hole 4 ofform 3 as above described. `The wire is permitted to rest in the left end of thread C. The wire, guided by the thread C, is wound from left to right, to form inner layer c: the wire is neXt guided by thread E and y advanced toward the left to form outer layer (l and section r2, then the wire is guided by thread D, continuing to the left, to form section r2. The unit may be wound beginning at -hole 5 and terminating at -hole l4, in which event coil 'c of section 43 will overlie coil d thereof.

The spacing of d is great'enough to permit c to enter between neighboring tur-ns into engagement with edge of form. 3.

In lieu of winding the section r3 ,of a single piece of conductor, it may be wound of two separate pieces. Referring to Fig. 4, the coll c of the section r3 may be a separate piece of conductor beginning at hole 4 and terminating at hole 4a near the end 1 of the resistance unit. The second piece of conductor may be looped through the hole 4a and Wound thereover in the same or reversed sense, which latter is indicated in Fig. 4a.

As a further modification the coil c, of separate conductor, may lbe -wound 'overlying coil d.

`The resistance unit-of Fig. 2, or of Fig. 4a, may be suitably mounted with relation to its control contact K as indicated in Figs. 5 and 6. A circular housing or casing 20, preferably of molded insulating material, such as bakelite, has an integral top 21 and base flange 22. Integral with the top is an annular ridge 23 spaced from the wall 20 to form an annular groove in which is set the resistance unit by bending it-into circular form. rlhe ends of the strip 3 are secured by bolts or screws 24 and 25 which constitute the terminals withwhich connectconnecting conductors 26, and 26a. The rotatable operthe resistance unit. A conducting member 30 maintains electrical contact with shaft 28 and therefore with contact K, and has its outer end secured to the casing 20 by the nut l3l which also serves as the binding post for the connecting conductor 32. W'hen the contact K is at the end 2 of the resistance unit R2 for a given amplitude of radio frequency energy absorbed by the antenna A the potential of grid g of the tube V is at a maximum. To reduce the volume the contact K is moved toward the end 1 of the resistance unit which reduces the potential of the grid of the tube.

AV, with a. consequent reduction in volume of reproduction of the loud speaker. As the contact K moves along the section r1 the resistance change per unit length of movement of the contact is of the same magnitude throughout traverse of that section, is less during traverse of section r2, and still less d uring traverse of section r3. The result is therefore a decrease of potential of the grid g of the tube V, as the contact K is moved from end 2 to the end 1. In the high volume region of control, adjacent the end 2, the change of resistance is relatively small per unit movement of the contact K and it requires no particular nicety of rotatable adjustment of knob 27 to effect desired change in volume. However, at the region of low volume control toward or ad? jacent the end 1 of the unit, to effect a given percentage change involume requires a much smaller change in impedance and 'this implies a smaller or nicer adjustment of the knob 27. To obviate such need for nicety of adjustment, the impedance change per unit of movement of the contact K is much less due to the increased spacing of .the section r?, and the double winding of section r3. By

utilizing a plurality of sections, and of proper length with respect to each other, a smooth and gradual change in volume control is possible, and particularly in the section r3.

A control resistance R2 of the character herein described may be utilized in other positions than that described. For example, such a resistance may be connected in shunt with the primary of one or more coupling transformers, as of T1, Fig 1. The resistance may also be utilized in shunt between the input elements of a tube, as the coupling tube v V, as disclosed in co-pending application Serial No. 249,785, above referred to.

It will be understood that the eect of section 713 of the resistance R may be varied, as by change of the relative pitches of the overlying layers or coi'ls thereof, and/ or by variation of material of either coil. Furthermore the pitchA of either or both coils o or d may vary as it progresses along the form. The lengths of the sections r1, r2 and f3 may vary, although if, for example, the coarse winding of section r3 is unduly shortened, there would be an abrupt change in volume, noticeable v as a click in the loud speaker, as the contact K passes from one section to the other.

While' preferably the component part c of section r3 is a'coil wound on strip 3 as a form, it may consist, for example, of a coil threaded through holes 33 in strip 3, as in Fig. 7, and part d lwound thereover around the edges of form 3, as before, and in such case the/pitch of 7'1 and (l may be the same. i

What I claim is:

1. A variable resistance unit comprising overlying conductor helices, the turns of different helices intersecting and electrically contacting each other, and a co-operating movable contact.

2. A variable resistance unitcomprising overlying conductor helices of dierent pitches each having a plurality of turns in electrical contact with turns of the other, and a co-operating movable contact.

3. A variable resistance unit comprising overlying electrically contacting conductor 4helices wound in opposite axial directions,

and a (co-operating contact. 4. A variable resistance unit comprising overlying conductor helices, the turns of different helices intersecting and electrically contacting each other, and a contact movable in engagement with the turns of the dillerent helices.

5.A A variable resistance unit comprising `overlying conductor helices of different pitches in electrical contact with Ieach' other, and a contact movable in engagement with the turns of the dierent helices.

6. A variable resistance unitcOmprising .helices of different pitches woundv in opposite axial directions, and a co-operating mov- -able contact. I

8. A variable resistance un1t comprlsing overlying electrically contacting conductor helices of dierent pitches wound 1n op osite axial directions, and a. contact `1nova le in engagement with the turns of the dierent helices.

9. A variable reslstance un1t comprlsing a .form, spaced turns of continuous conductor thereon, differently spaced turns of continu- .ous conductor overlying said turns and in electrical contact therewith, and a contact movable in-engagement with said turns.-

10. A` variable resistance unit' comprising a form, spaced turns of continuous conductor thereon, spaced turns of continuous conductor wound over and intersecting said turns-in electrical contact therewith, and a contact movable in .engagement .with said turns.

11. A variable resistance unit comprising a form, spaced turns of conductor thereon, differently spaced turns of conductor wound over said turns in electrical contact therewith and in a reverse direction along said form, and a contact movable in engagement with said turns.

12. The method of producing a resistance unit for a volume control rheostat, which comprises winding a conductor'in the form of a hel1x,'w1nd1ng over sald helix a conductor helix of different pitch and in electrical con- 14. The method of producing a *resistance unit for a volume control rheostat, which comprises winding a conductor upon and to- .wards one end of a form, and 'thereafter winding conductor towards the other end of said form inoverlying intersecting and electrically contacting relationwith said rst named conductor.

15. The method of producing a resistance unit for a volume control rheostat, which comprises windinga layer ofconductor upon and towards one end of a form with predetermined spacing between turns, and thereafter winding conductor with different spacing betweenturns towards the' other end of said vform in overlying and electrically contacting relation with said first named conductor.

JOHN M. MILLER. 

